The effect of apparent cross-link density on cut and chip wear in natural rubber

Abstract

Natural rubber is a polymer that, by inducing crystallization at a certain level of stress, contributes significantly to reducing cut and chip (CC) damage to rubber articles when exposed to harsh conditions. This unique property is dependent on several factors, including the processing conditions, the cross-linking system and the type of additives used, resulting in varying apparent cross-link density (CLD) of the cross-linked CB filled rubber. Therefore, this work focuses on the systematic investigation of CC phenomena as a function of CLDs represented by conventional (CV), semi-efficient (SEV) and efficient (EV) cross-linking systems. Rubber samples based on different cross-linking systems were prepared by varying the concentration of the accelerator N-tert-butylbenzothiazolesulfonamide (TBBS) at a constant concentration of 2.5 phr sulfur as a cross-linking agent. The different CLDs were achieved by different concentration ratios (A/S) between accelerator (A) and sulfur (S), using A/S = 0.1, 0.3, 0.6 for the CV system, A/S = 0.7, 1.0, 1.5, 2.0, 2.5 for the SEV system and A/S = 3.0 for the EV system. First, the basic mechanical behaviour was presented as a function of CLD, with the optimal behaviour found in the range of 181-241 mu mol x cm(-3). The CC resistance is independent of the CLD when the rubber specimens are loaded with a normal force of 100 N. However, at higher load, the optimal range of CLD decreases rapidly from 136 to 241 mu mol x cm(-3). Furthermore, a significant influence of SIC on CC resistance was confirmed in the range of CLD from 181 to 241 mu mol x cm(-3). Moreover, in the range of CLD from 181 to 241 mu mol x cm(-3) the predominant effect of NR on CC resistance was observed. Finally, an effect of degradation of cross-link network on CC properties due to rubber curing in the reversion has been discussed.